1. Field of the Invention
The invention relates to a power sensor, especially a diode detector.
2. Discussion of the Background
Conventional power sensors use discrete detector diodes arranged in a hermetically encapsulated housing on a substrate, whereas the substrate is disposed in close thermal contact with the housing. Because of its high mass of, for example, 50 g, such a metallic housing provides a high thermal capacity. This leads to a high time constant with regard to a reaction to changes in temperature, if the housing were to be heated. Beyond this, a considerable thermal power would be necessary in order to heat the large mass.
With diode sensors, such as those shown in DE 100 39 665 A1, temperature fluctuations lead to various negative effects on the measurement result. For example, on the one hand, the zero-point resistance of the diodes is temperature dependent. This leads to different terminating resistances and accordingly to different reflection coefficients. In the case of Schottky diodes, a resistance-dependence of −4%/K is provided, for example. That is to say, with a temperature change of 15 K, the zero-point resistance of the detector diode is halved. Furthermore, the noise behavior of the detector diodes is also temperature dependent.
To prevent a falsification of the measured values of the diode detector resulting from its temperature dependence, compensation circuits are used. For instance, EP 1 026 822 B1 discloses a diode detector with compensated temperature drift. The disadvantage here is that the compensation cannot, on the one hand, eliminate all residual errors, and, on the other hand, a noise behaviour and reflection behaviour of the detector influenced by temperature changes cannot be compensated by this compensation.
Furthermore, the Japanese patent JP 10 267 970 A shows a power detector embodied as an integrated circuit. A heating diode is integrated in the integrated circuit. In this context, the high-frequency signal is supplied through a hollow conductor. The integrated circuit is disposed in an interruption of the hollow conductor. Part of the power of the high-frequency signal is received and supplied to the power detector by means of antennas which are also a part of the integrated circuit. The disadvantage here is that this structure is only suitable for supplying the signal by means of a hollow conductor.